Rock Mass Failure Research Articles

Slope Mass Rating (SMR) Classification for Rock Slope Stability and Geohazard Vulnerability Assessment

Quantitative classification from the Slope Mass Rating (SMR) has introduced an empirical assessment for rock slope stability rating. This stability classification enables us to foreseethe magnitude and susceptibility of rock mass failure towards adjacent infrastructure and human life. In this study, the stability of quarry rock slope was classified using SMR classification system and kinematic stability analysis before being correlatedwith geohazard vulnerability assessment. Geological formation study with site geographical survey from aerial photogrammetry technique provided comprehensive data for the study area. Fieldwork to evaluate the SMR assessment parameters was conducted by discontinuity mapping using scanline method. In-situ evaluation of rock mass such as rebound surface hardness and discontinuity characterization was carried out with rock material sampling for laboratory testing. Kinematic stability analysis presented an estimation for the direction and mode of rock slope failure. The SMR classification that constitutes geomechanics attributes had introduced the global stability rating of rock mass structure, thus facilitating the prediction of potential failure magnitude. Hence, the integration of these stability indications provides sufficient empiricalestimation for geohazard vulnerability zoning for the studied area.

A Test Method for Finding Early Dynamic Fracture of Rock: Using DIC and YOLOv5.

Intelligent monitoring and early warning of rock mass failure is vital. To realize the early intelligent identification of dynamic fractures in the failure process of complex fractured rocks, 3D printing of the fracture network model was used to produce rock-like specimens containing 20 random joints. An algorithm for the early intelligent identification of dynamic fractures was proposed based on the YOLOv5 deep learning network model and DIC cloud. The results demonstrate an important relationship between the overall strength of the specimen with complex fractures and dynamic fracture propagation, and the overall specimen strength can be judged semi-quantitatively by counting dynamic fracture propagation. Before the initiation of each primary fracture, a strain concentration area appears, which indicates new fracture initiation. The dynamic evolution of primary fractures can be divided into four types: primary fractures, stress concentration areas, new fractures, and cross fractures. The cross fractures have the greatest impact on the overall strength of the specimen. The overall identification accuracy of the four types of fractures identified by the algorithm reached 88%, which shows that the method is fast, accurate, and effective for fracture identification and location, and classification of complex fractured rock masses.

Small Block Model Tests for the Behaviour of a Blocky Rock Mass Under a Concentrated Rock Anchor Load

Rock anchors are used to stabilise large-scale infrastructure such as the foundations of high buildings or road cuts, and their failure could lead to severe economic and social consequences. A rock anchor can fail in one or more of the following four modes; breakage of the tendon steel, tendon-grout bond failure, grout-rock bond failure and rock mass failure. In current rock anchor design, the knowledge for the first two failure modes is satisfactorily known and is relatively easy to test. The scientific background for the last two failure modes still has a potential of improvement and further development of the design criteria is needed. To help fill this gap, a series of block model tests were conducted on a small-scale test apparatus to evaluate the load capacity of a blocky mass under a rock anchor load. Digital image correlation (DIC) was used to monitor the full-field displacements in the block models. The tests showed that load arches were formed in the block layers and the anchor load was transferred to the side frames of the apparatus through these arches. The load capacity of the mass increased with the number of the block layers and the confinement. The observed load arches and the effect of the confinement were also captured in a numerical model using UDEC software. The DIC monitoring showed that the displacements in the block model were identical along a vertical line. At a given depth, the displacements decrease with the distance to the centre line of the anchor.

Experimental Study on the Damage Characteristics and Fracture Behaviour of Rock-like Materials with Weak Interlayer Zones

To study the effect of the dip angle of the weak interlayer zone (WIZ) on the damage characteristics and fracture behaviours of rock-like samples, a series of uniaxial compression tests were conducted, accompanied by acoustic emission (AE) tests and the digital speckle correlation method (DSCM). The experimental results indicate that the stress—strain curves before the peak can be divided into plastic—elastic—plastic and elastic—plastic curves, and the stress—strain curves after the peak can be divided into plastic failure, transitional failure and brittle failure curves. The relationship between the peak stress and peak strain and WIZ angle can be well described by two linear functions. As the angle increased, the specimen gradually changes from tensile failure to shear failure, and the number of cracks and falling fragments decreases gradually. In addition, it becomes difficult to predict rock mass failure by AE when the WIZ angle is close to 60°. The AE counts decrease with an increasing angle, reach a minimum at 60°, and then increase. Furthermore, the WIZ plays a key role in the deformation of upper hard rock.

Critical damage threshold of brittle rock failure based on Renormalization Group theory

An in-depth understanding of damage threshold behavior during rock damage and failure is critical to predicting short- and long-term rock stability. The percolation theory was used to describe the rock damage threshold behavior and the Renormalization Group theory was used to accurately solve the theoretical solution of the critical threshold of brittle rock failure. By redefining the stress-transfer mechanism between rock blocks, the theoretical expression of the critical damage threshold of brittle rock failure was calculated based on the Renormalization Group theory. An experimental investigation of shale samples by in-situ micro-computed tomography was carried out to verify the theoretical expression. The values of damage calculated experimentally were consistent with the theoretical critical damage threshold of brittle rock failure. On this basis, the reasonable range limit of the critical damage threshold for rock mass failure was discussed. The laboratory test results on different lithologies and case studies of in-situ direct shear tests of rock and rockfalls in Mesnil-Val were analyzed to validate the feasibility of the threshold range and reveal the potential application of the research results.

Mechanical Behavior and Failure Process of Hard Rock with Rock Bridge under Uniaxial Compression Test

Abstract The mechanical properties of rock mass are mostly controlled by the structural plane. Rock bridge has an important effect on the failure and stability of rock mass with structural plane. In this paper, the uniaxial compression test of hard rock containing rock bridge is carried out, accompanied by acoustic emission (AE) and high-speed video monitoring. Within the scope of this study, the results show that the uniaxial compressive strength (UCS) of sample with rock bridge increases with the rock bridge length. Under the same stress condition before peak, the strain of the sample decreases with the increase of the rock bridge length (RBL). Under the influence of stress concentration, the cracking of the sample starts from the prefabricated crack tip. The peak AE count of the sample decreases with the increase of RBL. The AE cumulative energy of the sample increases with the increase of RBL. The number of cracks in the sample before the peak is small, and the rapid increase of cracks is mainly concentrated in the main fracturing stage after the peak, while after reaching the residual stage, the increase rate of various types of microcracks in the sample is relatively slow. The numerical simulation results show that the number of all kinds of cracks in the sample before the peak is small, and the number of tensile cracks in the sample is very close to the total number of cracks under different RBLs. With the increase of RBL, the tensile/shear crack ratio decreases. The internal cracks of the sample are mainly concentrated at the peak stress and postpeak stage. The research results of this paper are of great significance to the engineering excavation and safe construction of jointed rock mass engineering.

Precursor Information Recognition of Rockburst in the Coal-Rock Mass of Meizoseismal Area Based on Multiplex Microseismic Information Fusion and Its Application: A Case Study of Wudong Coal Mine

Abstract In recent years, the rockburst induced by steeply inclined coal seam mining in the Urumqi mining area has become serious. In this paper, the evolution law of multiplex microseismic information before and after the rockburst is obtained through in-depth mining of the field microseismic data. In addition, the evolution characteristics of microseismic activities before and after the rockburst of steeply inclined coal-rock mass in the meizoseismal area are revealed from three important scales: time, space, and strength. The results show the following: (1) The microseismic activity of the Wudong Coal Mine is mainly of stress migration type. The sandwiched rock pillar is the primary inducement of rockburst, and the b value decreases greatly with the mining progresses (by 23.9%). It indicates that the risk of rockburst induced by the local failure of rock mass in this area is increasing. (2) From the time scale and strength index, the precursory indexes of rockburst are put forward, respectively: ① the daily total energy and the frequency of microseisms suddenly rise and fall rapidly at the same time in the shock start-up period (5 days before rockburst), and the daily total energy of microseisms decreases to the abnormal valley value within 30 days. ② The abnormal growth rate of microseismic events exceeded 60% in a certain stage, and “induced shock events” appeared. (3) The shock risk is positively correlated with the decline rate of energy index, the growth rate of cumulative apparent volume, and Schmidt. It is determined that the rockburst will occur within 19 days after entering the shock early warning period. The results of prediction examples show that this method has a good prediction effect on rockburst in strong meizoseismal areas, which can provide a reference for rockburst prevention in the mining process in strong meizoseismal areas.

Impact of Depressurizing Boreholes on Energy Dissipation in Deep Roadway

Depressurizing borehole drilling is an effective approach to control the large deformation of deep roadway. It can transfer the high stress in the proximity of the roadway into the deep stable rock masses. However, it should be noted that the borehole drilling will inevitably cause the secondary damage to roadway. To determine the parameters of depressurizing boreholes, the degree of the secondary damage must be evaluated properly. Given that the rock mass failure is an unstable phenomenon driven by energy, it is of great use to reveal the disturbing impact of depressurizing boreholes on the roadway stability from the angle of energy dissipation. This is much more consistent with the failure nature of rock mass. Hence, an integrated method of laboratory test, numerical simulation, and theoretical analysis was used to study the disturbing effect of depressurizing boreholes on roadway energy dissipation. The equations of elastic energy and dissipated energy of rock cell grid were derived based on the energy principle and finite-difference algorithm, which was implemented into FLAC3D software by the FISH language. The numerical stress-strain and dissipated energy-strain curves of rock samples were verified by experimentally obtained data, and the whole deformation path from roadway excavation to instability was back-analyzed by the dissipated energy evolution. Based upon the energy model, the ratio of borehole diameter D to row spacing R ( D / R ) was selected as the variable to analyze the influence of borehole parameters on the depressurizing effect. The varying D / R leads to three depressurizing states: insufficient depressurization, sufficient depressurization, and overdepressurization. Increasing D / R will make the roadway transfer from insufficient depressurization to sufficient depressurization and finally to overdepressurization. The sufficient depressurizing state could be realized by adjusting the borehole D / R value, which is of great use to the roadway control. The D / R values of 1 : 6 to 1 : 2 were proposed for the test roadway, and D / R = 1 : 6 was applied in the field test, which achieved a well roadway control effect.

Damage Constitutive and Failure Prediction of Artificial Single-Joint Sandstone Based on Acoustic Emission

The effect law of deformation and failure of a jointed rock mass is essential for underground engineering safety and stability evaluation. In order to study the evolution mechanism and precursory characteristics of instability and failure of jointed rock masses, uniaxial compression and acoustic emission (AE) tests are conducted on sandstones with different joint dip angles. To simulate the mechanical behavior of the rock, a jointed rock mass damage constitutive model with AE characteristic parameters is created based on damage mechanics theory and taking into account the effect of rock mass structure and load coupling. To quantify the mechanism of rock instability, a cusp catastrophe model with AE characteristic parameters is created based on catastrophe theory. The results indicate that when the joint dip angle increases from 0° to 90°, the failure mechanism of sandstone shifts from tensile to shear, with 45° being the critical failure mode. Sandstone's compressive strength reduces initially and subsequently increases, resulting in a U-shaped distribution. The developed damage constitutive model's theoretical curve closely matches the test curve, indicating that the model can reasonably describe the damage evolution of sandstone. The cusp catastrophe model has a high forecast accuracy, and when combined with the damage constitutive model, the prediction accuracy can be increased further. The research results can provide theoretical guidance for the safety and stability evaluation of underground engineering.

Study on the Failure Mechanism of Strain Rockburst

Among the factors affecting rock mass failure, the stress state has the greatest influence on the mechanical behavior of rock. The mechanical behavior of rock depends on the change of stress path, and the stress of rock mass is closely related to deformation and failure. In order to study the influence of surrounding rock stress state on the failure mode of surrounding rock, based on the theory of elastic mechanics and fracture mechanics, this paper analyzed the stress state of surrounding rock element and crack propagation of surrounding rock, and estimated the potential failure mode of surrounding rock in different areas of a phosphate mine in Yichang. The results showed that: the surrounding rock element is affected by the gradient stress, and a larger stress gradient corresponds to a larger principal stress ratio and variation direction of the surrounding rock. The failure mode of surrounding rock is affected by the coupling effect of principal stress ratio and principal stress direction. Under the action of certain crack angle and appropriate confining pressure, different fracture mechanisms may occur in the surrounding rock compression. But the partition of surrounding rock failure mode region can predict the surrounding rock failure mode to a certain extent.

Different Toppling Bank Slope Failures under Hydrodynamic Action during Impoundment of the Miaowei Hydropower Station Reservoir

Toppling is a common deformation and failure phenomenon in the reservoir bank slopes of hydropower projects. This paper studies the genesis and evolution of different toppling bodies during water impoundment at the Miaowei Hydropower Station Reservoir on the Lancang River in southwest China. Toppling properties were determined and second failure characteristics analyzed in different reservoir impoundment stages. Different degrees of toppling deformation were primarily affected by the transverse bending stress, while the regional tectonic stress has been shown to have a significant effect on the transverse bending of the rock layers. Combined with the on-site investigation and monitoring results, the failure mechanisms of the different toppling deformation bodies were analyzed. The second failure of the toppling rock mass caused by the reservoir impoundment process is mainly the hydrodynamic splitting along fractures, wave impaction and softening on the slope foot. The transverse bending effect of gravity is transmitted upward through joint misalignment, rotation and slip, accelerating the speed of secondary toppling failure and forming a compression-shear failure along the toppling tension crack. A model to predict the scope and time of failure in the toppling deformation banks under the action of reservoir hydrodynamics was proposed.

Analysis on the evolution of frost heaving pressure of penetrating crack considering water content and migration

Frozen heaving failure of fractured rock mass is commonly encountered in engineering in cold regions, which is chiefly caused by the frost heaving pressure arising from the water–ice phase change in the crack. To explore the evolution of frost heaving pressure in penetrating elliptical crack considering water content and water migration, a new theoretical model embodying the frost heaving pressure evolutionary character was established by introducing freezing ratio function. The equivalent thermal expansion coefficient was used to analyze the evolution process of frost heaving pressure under the effect of water–ice phase change, which was then verified. It was found that the evolution process of frost heaving pressure can be divided into three stages: free expansion stage of water–ice phase change, rapid growth stage of frost heaving pressure, and stable stage of frost heaving pressure. Subsequently, the influences of rock thermal expansion effect, properties of rock and ice, and water content of crack on the frost heaving pressure were investigated. The results indicate that the impact of rock thermal expansion on frost heaving pressure is extremely slight, which is negligible. Comparing with the properties of rock, the properties of ice show significant effects on the frost heaving pressure, particularly the Poisson ratio of ice. In the case of identical water migration ratio, the peak frost heaving pressure increases linearly with the water content of crack.

A Study on the Freeze–Thaw Damage and Deterioration Mechanism of Slope Rock Mass Based on Model Testing and Numerical Simulation

Engineering rock mass in cold regions has obvious freeze–thaw damage as a result of extreme differences in temperature, rainfall, snow, and other factors, which is one of the main causes of frequent geological disasters. Therefore, it is important to investigate the deterioration mechanism and evolution laws of rock mass freeze–thaw damage. Considering a hydropower station’s left bank slope in a cold region, model testing and numerical testing of slope rock mass failure under freeze–thaw conditions are here carried out by developing a generalized model. The results reveal that heat is transmitted from the outside to the inside of the slope and that the rate of temperature change varies with depth; the frost-heave force causes tensile cracks in the rock mass, with crack propagation taking the form of a circular arc; the presence of an original structural plane influences the propagation direction of the frost-heave crack, whereas the freezing rate of the fissure water influences the amplitude and growth rate of the frost-heave force. Additionally, a novel method of measuring frost-heave force is proposed. The largest frost-heave force caused by water–ice phase change is 19.3 kPa, which is equivalent to 3.17 MPa of the actual slope.

Fractional creep model of temperature-stress-time coupled damage for deep coal based on temperature-equivalent stress

The effective stress concept of temperature equivalent stress and actual stress acting together is established from the point of view that stress and temperature cause the same strain. The yield failure of coal and rock mass arises from the effective stress formed by the combination of temperature equivalent stress and actual stress. A temperature-stress coupled damage variable is established according to the hypothesis that the strength of coal and rock microunits obeys Weilbull distribution law and meet Drucker-Prager (D-P) yield failure criterion. A temperature-stress-time coupled damage variable is established by introducing a negative exponential function related to temperature and actual stress duration. The temperature-stress coupled damage variable of coal and rock mass is independent of the action time of temperature and time, but only related to the yield function F. The time damage variable is associated with the action time after the effective stress reaches the yield, which is mainly manifested in the viscoplastic deformation. Uniaxial and triaxial fractional creep models considering temperature-stress-time coupled damage are established by using Caputo fractional derivative definition. The parameters of temperature-stress-time coupled damage creep model are obtained by fitting the laboratory test data of deep coal body. The sensitivity of fitting parameters to the model and the goodness of fit analysis show that temperature-stress-time coupled damage model can well demonstrate the creep curves under different temperatures and stresses and the fitting accuracy is high.

Three-dimensional modeling and analysis of fractal characteristics of rupture source combined acoustic emission and fractal theory

Deep mining exploration and the sustainable use of enormous data via acoustic emission (AE) systems is a major experimental approach for fulfilling the perception, characterization, and forecasting for rock engineering catastrophes such mines, tunnels, and water conservation. To carry out the fine numerical characterization of the nonlinear and disordered time-space-energy information in the AE system, we use the fractal theory to analyzing. The key elements such as time, space, and energy of the fracturing source are comprehensively extracted. The fractal dimension statistical framework and its optimal dimension are designed, and the three-dimensional (3D) analysis model that can characterize the actual failure and instability process is constructed. The AE experimental data and numerical simulation are used to obtain the spatial clustering and energy dissipation fractal dimension characteristics of regional AE events in the time domain. The model is optimized and verified on the spot. The results show that the time-space-energy parameters of AE can be characterized by fractal dimension. The fractal dimension analysis model can transform and finely characterize the failure anomaly data. The distribution results of the fractal dimension value field can be consistent with the actual failure. Through iterative optimization and comprehensive verification of the scientificity and applicability of the fractal dimension analysis model, a comprehensive fractal dimension representation method of time-space-energy of fracture source in rock failure process is formed, which can provide guidance for the service and analysis of existing monitoring systems in mines, and provide theoretical support and technical conditions for fine judgment of rock mass failure in mines.

Experimental evaluation of precise monitoring of multi-scale deformation failure of rock mass based on distributed optical fiber

To realize the precise monitoring of multi-scale deformation and failure of rock mass by distributed optical fiber, the mechanical model of optical fiber and rock strata is established to analyze the mechanical characteristics and strain response of rock strata under the stages of elastic deformation, elastoplastic deformation. Finally, an optical fiber quantitative monitoring method for multi-scale deformation and failure of rock strata is presented to quantify the deformation characteristics of rock mass at different scales and failure modes in different regions. On this basis, the distributed optical fiber is embedded in a similar model to monitor the internal deformation of the strata of the model. Meanwhile, Digital image correlation (DIC) is used to observe the deformation of the strata in real-time to verify the accuracy of the proposed method. The research results can promote the application of optical fiber sensing technology in the field of mine engineering.

Experimental Investigation of Failure Mechanisms of Granites with Prefabricated Cracks Induced by Cyclic-Impact Disturbances

Engineering rock mass is normally subject to cyclic–dynamic disturbances from excavation, blasting, drilling, and earthquakes. Natural fractures in rock masses can be reactivated and propagated under dynamic and static loadings, which affects the stability of rock mass engineering. However, fractured rock mass failure induced by cyclic-impact disturbances is far from clear, especially considering varying angles between the rock mass and the direction of impact loadings. This work investigated rock deformation and failure characteristics through cyclic impact tests on granite samples with cracks of different angles. A Hopkinson bar was employed for uniaxial cyclic impact tests on granite samples with the crack inclination angles of 0–90°. The magnetic resonance imaging technique was used to determine rocks’ porosity after cyclic impacts. The stress–strain curves, porosity, strength, deformation modulus, failure modes, and energy density of samples were obtained and discussed. Results showed that the crack inclination angles significantly affected the damage evolution and crack morphology of rocks. Under the constant cyclic impact, the dynamic deformation modulus and dynamic strength of rock samples first increased and then decreased with the increase in crack inclination angle. The failures of granite samples for inclination angles of 0 and 90° were dominated by tensile cracking, while those for the inclination angles of 30–60° were dominated by shear cracking. The energy density per unit time gradually decreased with the increase in impact cycles. The results can provide references for the stability analysis and cyclic-impact-induced failure prediction of fractured rock masses.

A Field Study on the Law of Spatiotemporal Development of Rock Movement of Under-Sea Mining, Shandong, China

The phenomenon of rock movement in mining areas has always been a difficult problem in mining engineering, especially under complicated geological conditions. Although the backfilling method mitigates the destruction of the surrounding rock, deformation can still exist in the mining area. In order to ensure the safety of under-sea mining, it is necessary to study the rock movement laws and the mechanisms. This paper focuses on a settlement analysis of the monitoring data of the No. 55 prospecting profile. By analyzing the shape of the settlement curves, the spatial distribution characteristics of settlements of different mining sublevels are summarized. Additionally, the fractal characteristics of the settlement rate under different space–time conditions are studied. We also discuss the relationship between the fractal phenomenon and the self-organized criticality (SOC) theory. The findings are of great theoretical value for the further study of mining settlements to better understand the physical mechanisms of internal movement and rock mass failures through the fractal law of the settlement. Furthermore, elucidating the rock movement law is an urgent task for the safety of seabed mining.

Evolution Characteristics of Seismic Detection Probability in Underground Mines and Its Application for Assessing Seismic Risks-A Case Study.

Seismic hazards are typical mining hazards causing dynamic failure of coal and rock mass, which greatly threatens the safety of personnel and equipment. At present, various seismic analysis methods are used to assess seismic risks but their accuracy is significantly limited by the incompleteness of seismic data. The probability of detecting earthquakes (PDE) method has been proven as a powerful means for retrieving missed seismic events and enhancing the seismic data integrity in mines. However, to date, the reliability of the results of the PDE method has not been assessed and the highly integrated seismic data have not been linked with the actual hazard potential. To fill these gaps, this paper investigated the impacts of the seismic data volume used for calculation and the modification of the layout of sensors on the reliability and robustness of the PDE method. The event counts and seismic energy were compensated using the PDE method, correlated with strong seismic events. The results indicated that the compensated seismic data presented higher accuracy in locating future hazardous events than before. This research provides references on enhancing the performance of seismic analysing methods for seismic risk assessments.

Effect of Crack Angle and Length on Mechanical and Ultrasonic Properties for the Single Cracked Sandstone Under Triaxial Stress Loading-Unloading

The disturbance due to coal mining causes the surrounding rock to undergo a complex process of stress changes during which the axial pressure and the confining pressure usually change accordingly at the same time. Existing studies generally investigated this process from a static perspective, which was not rigorous. The mechanical characterization of rock is very important to understand the failure of rock mass and the safety of mining during mining disturbance. Based on theoretical analysis, we conducted axial loading and radial unloading tests on the cracked sandstone, which was combined with the ultrasonic testing technology to examine its failure rules and to characterize and analyze its failure process using longitudinal wave velocity. The results demonstrated that crack length and angle had a significant impact on the strength and mechanical properties of sandstone, and the former had a greater impact on the strength of sandstone than the latter. As the crack length increased, the strength, elastic modulus, and deformation modulus of sandstone decreased, and the strength of sandstone increased as the crack angle increased. Elastic and deformation moduli first decreased and then increased. Furthermore, Poisson’s ratio increased slowly, then decreased slowly, and finally increased rapidly as the lateral pressure coefficient diminished, and Poisson’s ratio was more sensitive to changes in the angle. In this study, the change of longitudinal wave velocity reflected the whole process of sandstone failure. When the wave velocity was stable, the rock was at the yield limit point. Moreover, when the wave velocity was unstable, the sandstone was in a progressive failure period, and as a result, the wave velocity decreased and the sandstone cracked.